1. Field
This invention relates generally to a system and method for optimizing a constellation for digital signal coding and transmission and, more particularly, a system and method for optimizing a constellation for digital signal coding and transmission for a satellite communications channel that employs minimizing a difference between a rate of symbol-wise mutual information between a transmitted constellation symbol and a rate of an unconstrained capacity to determine the number of rings, the number of symbols in each ring, and the ring ratio in the constellation.
2. Discussion
Satellite communications is seeing a growing demand for greater throughput and transponders with more DC power efficiency. To provide greater spectral efficiency, satellite communications systems often employ modern coding and modulation, which is best exemplified by the known digital video broadcasting (DVB)-S2 standard and protocol. Code concatenation is an effective way to achieve large coding gains while maintaining the decoding complexity to be manageable. However, ever since the discovery of “turbo-codes” it has been widely acknowledged that the iterative processing techniques are not limited to conventional concatenated error correction codes, and the so-called “turbo principle” is more generally applicable to many other components found in modern digital communications. One such example is iterative de-mapping and decoding in coded modulation communication systems. Coded M-ary amplitude phase shift keying (M-APSK) is the “de-facto” bandwidth-efficient modulation technique for digital satellite communications.
In order to meet the radiated power demands necessary for the signal transmission distances, satellite communications systems employ high power amplifiers (HPAs), such as traveling-wave tube amplifiers (TWTAs) and solid-state power amplifiers (SSPA). To provide high throughput and increased efficiency, these HPAs often operate at or near their saturation level, which often results in severe non-linear distortions of the transmitted signal that has a reverse effect on the throughput and performance of the communications channel. M-APSK provides a power- and spectral-efficient solution with its inherent robustness against highly non-linear distortion. However, the implementation of satellite communications channels still provides significantly different design challenges from traditional terrestrial channels due to their dominant non-linear behavior.